I. Field of the Invention
The present invention relates generally to the field of high pressure hydraulic pumping applications. More particularly, the present invention relates to an improved valve assembly for automatically priming a hydraulic pump during a suction-fed application wherein the pump must draw fluid from within a holding tank for subsequent pressurization and transmission by the pump. The valve assembly of the present invention is provided in fluid communication with the outlet line of the pump and offers a path of least resistance for the air within the pump and the suction hose before automatically shutting off when fluid has been drawn into the pump.
II. Discussion of the Prior Art
The first step in initiating hydraulic pumping operations entails priming the pump to introduce fluid into the various pumping cylinders therewithin such that the fluid may be subsequently propagated away from the pump. Perhaps the most routine and least burdensome approach to priming hydraulic pumps involves supplying water to the pump in a pressure-fed fashion, wherein pressurized fluid is fed directly into the inlet line of the pump. In most pumping applications, pressurized water is produced by public water utilities which typically provide water lines carrying water pressurized to between 40 and 60 pounds per square inch (psi). The pressurized fluid works to supplement the suction force generated within the pumping cylinders to thereby collectively displace all the air from within the pump. Supplementing the suction force of the pump with pressurized water is advantageous in that, with these combined forces, the pump does not have to work as hard to draw the fluid into the internally disposed pumping cylinders.
However, not all pumping applications allow for the introduction of pressurized fluid into the inlet line of the particular hydraulic pump. For example, in the interest of isolating the public water supply from high pressure pumping operations, Japanese law requires that a holding tank be provided in between the public water line and the inlet line of the pump. Such an arrangement is shown in FIG. 1, wherein a hydraulic pump 10 is provided in combination with a suction hose 12, a holding tank 14, an unloader valve 16, a connecting hose 18, and a spray gun 20 for engaging in a high pressure spraying application. The suction hose 12 has a first end connected to the inlet port of the pump 10 and a second end which extends below the water line within the holding tank 14. The spray gun 20 is provided with a nozzle 22 of reduced diameter for producing back pressures of up to 3000 pounds per square inch or higher within the connecting hose 18. In this arrangement, the pressurized water from the public water supply is not capable of supplementing the suction force of the pump 10 which, in turn, causes the pump 10 to bear the entire burden of drawing water into the pumping cylinders to displace the air within the pump 10 for priming purposes. While this is effective in isolating the public water supply from potential contamination, several substantial drawbacks stem from the requirement of having a holding tank in between the public water supply and the pump.
The first notable disadvantage to restricting a hydraulic pump to such a suction-fed arrangement is that it is very difficult for the pump 10 to create enough suction force to draw water from the holding tank 14 to displace the air within the pump 10. The first reason for this stems from the substantial volume of air that exists within a high pressure pumping system prior to start-up. When the pump 10 is initially started, the entire pumping system is filled with air, including the pump 10 and all components connected both upstream and the downstream therefrom. The upstream line includes the suction hose 12 from the holding tank 14 to the inlet port of the pump 10, while the downstream line includes the unloader valve 16, the connecting hose 18, and the spray gun 20. In order to prime the pump 10, it is necessary to draw water into both the upstream line (suction hose 12) and the pump 10 in an amount sufficient to displace all of the air therefrom. However, the volume of air within the downstream line presents a substantial amount of resistance for the pump 10 when it attempts to draw water from the holding tank 14 to displace the air from the suction hose 12 and the pump 10. This is because the connecting hose 18 is typically quite long and of small diameter. There is also a substantial amount of resistance within the downstream line because the trigger of the spray gun 20 is typically off at start-up such that the nozzle 22 is closed, thereby providing no escape outlet for the volume of air trapped within the unloader valve 16, the connecting hose 18, and the spray gun 20.
The difficulty in priming hydraulic pumps during suction-fed applications also stems from the high operating speeds of hydraulic pumps, as well as the relatively small displacement of each cylinder within hydraulic pumps. Hydraulic pumps typically run at speeds ranging from 3400 to 3600 revolutions per minute depending upon the particular the motor/engine employed, while the displacement of each particular cylinder within the pump is typically quite small, in the order of a fraction of a cubic centimeter per cylinder for each pumping stroke. As such, the displacement during each pump stroke is so small that the pump 10 is incapable of developing a collective suction force sufficient to draw the air out of the suction hose 12 and pump 10 in order to pull water into the pump 10 for priming purposes. This lack of suction power, taken in conjunction with the air trapped within the unloader valve 16, the connecting hose 18, and the spray gun 20, causes the task of priming suction-fed hydraulic pumps to take an extremely long time to achieve. For example, priming periods of up to 20 minutes have been experienced using the system illustrated in FIG. 1. During this time, the pumps are subjected to increased stress and heating due to the "dry" pumping with no fluid within the cylinders, thereby decreasing the effective life span of the particular pumps. In many instances, the pumps are totally incapable of achieving a fully primed condition such that the pumps suffer seal damage from overheating.
One approach at lessening the time required to prime and minimizing the likelihood of damaging the pump involves manually triggering the spray gun 20 at start-up so that the air trapped within the downstream line may escape through the nozzle 22 thereof.
However, this method is disadvantageous in that it presents added difficulty to the process of priming the hydraulic pump 10 by requiring a user to manually activate the trigger of the spray gun 20 to open the nozzle 22. Frequent triggering of the spray gun 20 is also disadvantageous in that it increases the time required to bring the pump 10 into a fully primed condition with the suction hose 12 and the pump 10 completely filled with water.
A problem also exists with the aforementioned suction-fed hydraulic pumping applications after the pump 10 has been primed in that a certain amount of undesirable heating occurs within the pump head when the unloader valve 16 is activated. As noted above, the unloader valve 16 acts to reduce the pressure within the pump head when the trigger of the spray gun 20 is released while maintaining the water within the connecting hose 18 and spray gun 20 at or near the full operating pressure of roughly 3000 psi. The unloader valve 16 does so by opening up a line of fluid communication between the inlet and outlet sides of the cylinders such that the water within the pump head is forced to circulate therewithin by virtue of the cylinders which remain pumping when the trigger is released. This continual circulation of water within the pump head is problematic from the standpoint of overheating because the water has no outlet from the pump head during the period when the unloader valve 16 is activated, and thereby successively increasing the temperature of the water as the pump 10 continues to churn a high rate of speed. This increase in the temperature of the water, in turn, causes the packings of the pump 10 to increase in temperature which may damage the structural integrity of the packings to a point where the pump 10 is no longer operable.
A need therefor exists for an apparatus for improving the priming of a suction-fed hydraulic pump. More particularly, an apparatus is needed for improving the degree to which a suction-fed hydraulic pump is capable of creating suction force to draw water from a holding tank to displace the air from within the suction hose and the pump to thereby prime the pump. The apparatus should be able to reduce the degree to which the volume of air within the downstream line of the pumping system presents resistance for the pump when it attempts to draw water from the holding tank to displace the air from suction hose and the pump. Specifically, the apparatus should be able to accomplish the aforementioned task of priming a suction-fed hydraulic pump regardless of the length of the connecting hose or the amount air disposed within the upstream line, the downstream line, and/or the pump by providing an escape outlet for air trapped within the complete fluid path. A need also exists for an apparatus for priming a suction-fed hydraulic pump which does not require a user to frequently trigger the spray gun in order to create an escape outlet for the air trapped within the upstream line of the pumping application, thereby decreasing the time that is required to bring the pump into a fully primed condition with the suction hose and the pump completely filled with water. Finally, a need exists for a suction-fed hydraulic pumping arrangement which provides a temperature dissipation feature so as to eliminate the undesirable and potentially damaging heating that may result when the unloader valve is activated such that the packings and pump head are more readily maintained at moderate temperatures to thereby increase the effective life span of the pump.